Further studies will be carried out on the effects of dietary proteins and amino acids on alpha-aminoisobutyric acid (AIB) transport in rat liver. These experiments will include investigations of possible effects of undernutrition. After feeding rats low or non-protein diets for varying time periods the animals will be fed a single meal of a high-protein diet, or treated with hormones such as glucagon; hepatic cyclic AMP and AIB transport will then be determined to observe if the usual increases seen after these treatments in well-nourished rats are altered in the undernourished state. If prior lack of dietary protein decreases the response to one high protein meal or to glucagon, studies will also be carried out to determine the time needed for reversal of this effect. Since variations in brain amino acid pools can be caused by dietary treatments, experiments will be conducted to determine if alterations in amino acid transport in brain slices can be produced by the prior feeding of amino acid imbalanced diets or diets containing high levels of individual amino acids. Such experiments may provide evidence for the suggestion that the altered pools are partly due to effects on transport mechanisms.